Is your soil not sufficiently acidic? Using iron chelate is considered as a stop gap method of addressing iron chlorosis and will be a temporary 'fix' at best. It is far more effective to correct soil acidity (if possible) so that the Fe accessibility is resolved. That too will be a temporary measure if the pH needs to be lowered signficantly.

Since the plant is winding down for the season and no longer heavily photosynthesizing, waiting untl spring would be better than applying now. But realize that unless the pH issue is resolved, you wll need to reapply the chelated iron every few weeks.

btw, most fertilizers forumlated for acid loving plants will also contain soluble Fe.

I'm probably guilty of over-watering during the summer. This is a new plant (Encore Azalea), its first summer. I amended the soil before planting, so it's probably not the lack of acid. However, the other azaleas in the same bed look okay, maybe a little over-watering for them as well, but they fared much better.